The invention relates to a method for regulating the throughflow through a bottom nozzle of a metallurgical vessel. Furthermore, the invention relates to a bottom nozzle of a metallurgical vessel.
In particular, in steel melting the liquid metal is cast from a distributor, for example in a continuous casting plant. It flows through a bottom nozzle arranged in the floor of the distributor housing. Adherence of material to the wall of the bottom nozzle during throughflow is disadvantageous. The cross section of the aperture is thereby decreased, so that the flow properties are disadvantageously affected. To prevent the adherence of material to the wall, an inert gas, such as argon, is often introduced into the throughflow aperture. However, excessive amounts of gas negatively affect the steel quality, for example by the formation of cavities in the steel which lead to surface defects when the steel is rolled.
A material for a bottom nozzle is described, for example, in International patent application Publication No. WO 2004/035249 A1. A bottom nozzle within a metallurgical vessel is disclosed in Korean published patent application No. KR 10 2003-0017154 A or in U.S. published patent application Ser. No. 2003/0116893 A1. In the latter publication, the use of inert gas is shown, with the aim of reducing the adherence of material to the inner wall of the bottom nozzle (so-called clogging); this is similarly described in Japanese published patent application (Kokai) No. JP 2-187239. A mechanism with a gas supply regulation is known in detail from International patent application Publication No. WO 01/56725 A1. Nitrogen is supplied according to the Japanese Kokai No. JP 8-290250. Japanese Kokai No. JP 3-193250 discloses a method for observing the adherence or clogging of material with the aid of numerous temperature sensors arranged one behind the other along the bottom nozzle. The introduction of inert gas into the interior of the bottom nozzle is further known from, among others, Japanese Kokai Nos. JP 2002-210545, JP 61-206559, JP 58-061954, and JP 7-290422. It is furthermore known from a few of these publications, in addition to the introduction of inert gas, to prevent the access of oxygen as far as possible by using housings around a portion of the bottom nozzle. An excess pressure of inert gas is partially produced within such a housing, as disclosed, for example, in JP 8-290250.
A housing around a valve of the bottom nozzle, to prevent the entry of oxygen, is disclosed in Japanese Kokai JP 11-170033. The throughflow of the metal melt through the bottom nozzle is controlled by sliding gates, according to the above-mentioned publications. These sliding gates slide perpendicularly to the throughflow direction of the metal and can thus close the bottom nozzle. Another possibility for throughflow regulation is a so-called plug bar (also termed stopper rod), as known, for example, from Japanese Kokai JP 2002-143994.
In the Korean published patent application No. KR 10 2003-0054769 A, the arrangement of a housing around the valve of a bottom nozzle is described. The gas present in the housing is sucked out by means of a vacuum pump. Japanese Kokai JP 4-270042 describes a similar housing. Here, as in others of the above-mentioned publications, a non-oxidizing atmosphere is produced within the housing. The housing has an aperture through which the inert gas can be supplied. A further arrangement, in which the gas is sucked out of the housing partially surrounding the bottom nozzle, in order to produce a vacuum within the housing, is known from Japanese Kokia JP 61-003653.